This invention generally relates to a magnetometer for a torque sensor. More particularly, this invention relates to a magnetometer including several coils disposed relative to each for measuring torque related divergent magnetic fields.
Conventional torque sensors include a torque transducer element that responds to the application of torque by generating a magnetic field. Such generated or changed magnetic fields are detected by a magnetometer. The torque transducer element typically includes a magnetoelastic material that responds to the application of torque by generating a magnetic field. The application of torque to the magnetoelastic material creates shear stresses within the magnetized regions causing the direction of the magnet field generated by the torque transducer element to shift from a substantially circumferential direction to a helical direction. The helical shifting of the magnetic field is detected as an axial component of the magnetic field. The axial component of the magnetic field is proportional to the applied torque and provides an accurate and reliable indication of torque applied to a torque element.
Sensing of the magnetic field and specifically the axial components of the distortions in the magnetic field caused by torque is accomplished through the use of magnetic field sensors. A commonly used type of magnetic field sensors is a flux gate sensor, which is fabricated as a coil of fine wire surrounding a core of magnetically-saturable material, and is supplied with an alternating current. The alternating current provides for the periodic magnetic saturation of magnetic elements. The magnetic field produced by the torque transducer shaft is superimposed on the periodic magnetic field generated by the coils. The superimposing the magnetic field produced by the torque transducer shaft creates an asymmetry in the magnetic saturation of the coils. Changes in the inductance of the coils due to the magnetic saturation results in a voltage that is induced to the coils. It is this voltage that is measured to determine the amplitude and direction of torque applied to the torque transducer element.
A known prior art magnetic field sensor includes a bobbin having an upper and lower axial section provided by a central flange. The upper and lower coils are isolated from each other and are induced with an alternating current to produce a magnetic field. Magnetically saturatable strips are disposed between the coil and the torque transducer element. These magnetic strips are magnetically saturated by the alternating current that is produced within the coils. The magnetic strips are disposing parallel to the shaft and the axis of rotation. The magnetic strips are fabricated from a material that possesses a very abrupt magnetic saturation characteristic, meaning that the magnetic strips are quickly saturatable in the presence of a magnetic field and in the absence of the magnetic field quickly demagnetize.
Disadvantageously prior art magnetic field sensors require precise alignment to eliminate distortion caused by impinging magnetic fields. The required specific and precise alignment increases cost and complexity and reduces durability and dependability of the torque sensor.
Accordingly, it is desirable to design and develop a durable easy to produce and accurate magnetic field sensor that is compatible with torque transducer elements having a shaft supporting a magnetoelastic material.